1. Field of the invention
The present invention relates to a composition for a photo-reactive organic polymeric gate insulating layer and an organic thin film transistor using the same, and more particularly, to a composition for a photo-reactive organic polymeric gate insulating layer formed by mixing poly (vinyl) phenol as a material for organic polymeric gate insulating layer with a photo-reactive material to allow a photo patterning characteristic of the organic polymer and to enhance an insulating characteristic, and an organic thin film transistor using the same.
2. Discussion of related art
Worldwide researches have been actively conducted on organic thin film transistors using an organic material as an active layer since 1988.
The organic thin film transistor has a structure almost similar to that of a conventional silicon-thin film transistor (Si-TFT) but differs from the conventional structure in that it uses an organic material instead of silicon in a semiconductor region. A printing process or a spin coating process at an atmospheric pressure instead of physical and chemical vapor deposition methods employed for the formation of an inorganic thin layer of the conventional si-tft can be applied to manufacture the organic thin film transistor so that a manufacturing process can be simplified and the process can be carried out at a low temperature. When such advantages are employed, a roll-to-roll process using a plastic substrate can be implemented and it can also be applied to a large-sized flat panel display.
It is expected that the organic thin film transistor can be applied as an essential component of a plastic circuitry of a memory device included in an active matrix (AM) display, an automatic teller machine, an identification tag, and so forth. The organic thin film transistor can be easily assembled, has mechanical flexibility, and can be manufactured at a low temperature. The organic thin film transistor has several associated characteristics, and an efficiency of the organic thin film transistor is affected by a degree of crystallization of an organic active layer, a charge characteristic of an interface between an organic insulating layer and the organic active layer, a thin film characteristic of the organic insulating layer, carrier injection capability of an interface between the organic active layer and source and drain electrodes, and so forth. Several methods are thus attempted in order to improve such characteristics.
A material is required which has a low electrical conductivity and a high breakdown field to be used as a gate insulating layer of the organic thin film transistor. A silicon oxide layer has been in use up to now as the gate insulating layer of the organic thin film transistor, however, in order to lower a threshold voltage, the family of ferroelectric insulators including BaxSr1−x TiO3 barium strontium titanate (BST), Ta2O5, Y2O3, TiO2, and an inorganic dielectric material with a high dielectric constant such as PbZrxTi1−xO3 (PZT), Bi4Ti3O12, BaMgF4, SrBi2(Ta1−xNbx)2O9, Ba(Zr1−xTix)O3 (BZT), BaTiO3, SrTiO3, Bi4Ti3O12 are currently employed (see U.S. Pat. No. 5,946,551, Korean Patent Publication Nos. 2002-0084427 and 2002-0034873).
Up until now, the silicon oxide layer is used as the gate insulating layer of the organic thin film transistor, however, in a case of an inorganic insulating layer, it is formed at a high temperature so that it may affect a substrate (in particular, a plastic substrate) and physical/chemical properties of other layers formed on the substrate in a pre-process (hereinafter, a pre-process layer) to thereby affect the characteristic of the transistor when it is applied to the organic thin film transistor. Accordingly, researches on a new organic gate insulating layer are widely conducted which can implement a low temperature process to minimize an influence on the pre-process layer.
Polyimide (Korean Patent Publication No. 2003-0016981), poly (vinyl) alcohol (Korean Patent Publication No. 2002-0084427), poly(vinylphenol-maleimide) (Korean Patent Publication No. 2004-0028010), photoacryl and so forth are employed as the organic insulating layers in recent years, however, which did not exhibit a device characteristic enough to replace the conventional inorganic insulating layers. Accordingly, in order to implement an organic thin film transistor having high efficiency, development on an organic gate insulating layer having a good device characteristic and allowing a simplified process to form the thin layer without affecting the substrate and the pre-process layer as well as development on an organic active layer material are immediately required.
Accordingly, the present inventors have conducted a research on an organic polymeric gate insulating layer for implementing the organic thin film transistor with high efficiency, and have found that a layer can be formed which allows the photo patterning characteristics to be added to the organic polymer and allows the insulating characteristics to be enhanced when a photo-reactive material is added to poly (vinyl) phenol as the gate insulating layer material and that this can be applied to the organic thin film transistor to thereby yield an enhanced device characteristic.